That group describes itself as a means to “amplify progressive voices by providing an online and in-person campus for exchanging ideas and learning how to be more effective in using technology to influence the public debate.”

Biden said the jet seems to have been “blown out of the sky” by a missile, killing nearly 300 passengers. He called the situation “truly grave,” but noted that many questions still need to be answered.

“It’s important we get to the bottom of this sooner or later, because [of] the possible repercussions that could flow from this beyond the tragic loss of life,” said Biden, adding that officials with the US National Transportation Safety Board were headed to Ukraine to assist the international investigation.

In a statement, Poroshenko blamed the attack on separatist insurgents with strong ties to the Russian military.

“I would like to inform that one of the militants’ leaders was boasting of the downed aircraft in a conversation with his foreign Russian supervisor, colonel of the Main Intelligence Directorate of the General Staff of the Armed Forces of the Russian Federation Vasili Geranin,” Poroshenko said.

Biden then went on to discuss some progressive policy issues, including LGBT civil rights, voting rights, gender equality and climate change.

He also took on income inequality, telling the crowd to consider what they can do to create a “more fair, just and prosperous” America where everyone shares in productivity and wealth gains.

“He understood that when people get paid more, the economy grows,” Biden said.

“More products get bought. The rich get richer. The middle class grows. And the poor have a vision for a way up. But that bargain’s broken today.”

Biden’s speech was briefly interrupted by a group of young immigrant rights activists, who shouted “Stop deporting our families!”

Biden said he applauded the group’s message, and went on to praise immigrants as the “source of [America’s] ability to constantly remake ourselves.”

But he didn’t talk about specific immigration policy measures, or address the ongoing humanitarian crisis resulting from tens of thousands of Central American refugee children flooding the southern border.

Biden did hit on some broader, grander themes, though.

He told activists that in a time when “there are fundamental changes taking place in the world and at home,” passionate and principled individuals can “actually bend history a little bit.”

“We need to be crystal clear on the fundamental organizing principles we think this democracy rests upon, and fight like hell to make sure they are sustained and maintained,” Biden said. “Because it is on those organizing principles that we’re able to potentially build a much better, fairer nation.”